Determination of residual nickel in the culture broth after harvesting mycelial biomass from the metal-amended media revealed total removal of nickel by the increased biomass of the Trichoderma isolates at Ni concentrations of up to 40 ppm, followed by an increase in residual nickel and a decrease in biomass production at higher nickel concentrations in the medium. Among the isolates, IBT-I was most potent in biosorption of nickel, followed by UBT-18 and MT-4 (Fig. 5). The results are in agreement with the findings of Sarkar et al.,26 who recorded 90.2% removal of Ni from a 50 ppm-amended culture broth by T. harzianum after seven days of growth, beyond that, there was no increase in metal uptake. The use of a solid-phase extraction process to determine biosorption of heavy metals showed that 0.59 g of nickel could be removed by Aspergillus fumigatus from a liter of polluted water.35
The trend of cadmium biosorption was quite different, so that the increasing cadmium concentrations resulted in decreasing biomass production by all of the test isolates and positively correlated with increased residual cadmium in the culture broth (Fig. 6).
It has been suggested that metal uptake by T. harzianum is highly pH- and temperature-dependent and the maximum metal uptake takes place at pH 4.36,37 At pH values above 7, metal uptake is reduced as metals exist as hydroxide colloids